In the case of the directional valves this is the pressure difference between the pressure and tank connection of the valve in the case of short-circuited operating ports A and B of the valve. In the case of proportional directional valves, the nominal flow is stated at a 10 bar valve pressure drop, and for servo valves it is stated at a 70 bar valve pressure drop.
In the case of the continuously adjustable pressure valves: inlet pressure minus outlet pressure (EDIN 24 311).